Tissue distraction device

ABSTRACT

An apparatus and method for distracting, in a given direction, and supporting two tissue surfaces. A plurality of wafers are consecutively inserted between the two tissue surfaces to create a column of wafers. The column of wafers is oriented between the tissue surfaces so as to expand in the given direction as the wafers are consecutively added to the column.

[0001] This application claims the benefit of priority to U.S.Provisional Application No. ______, filed Mar. 8, 2001.

FIELD OF THE INVENTION

[0002] The present invention involves the field of surgery, andparticularly surgical instruments and methods of using the same.

BACKGROUND OF THE INVENTION

[0003] A variety of physical conditions involve two tissue surfacesthat, for treatment of the condition, need to be distracted from oneanother and then supported away from one another. Such distraction maybe to gain exposure to select tissue structures, to apply a therapeuticpressure to select tissues, to return tissue structures to theiranatomic position and form, or in some cases to deliver a drug or growthfactor to alter, influence or deter further growth of select tissues.Depending on the condition being treated, the tissue surfaces may beopposed or contiguous and may be bone, skin, soft tissue, or acombination thereof. An optimal treatment method includes distractingand supporting the tissue surfaces simultaneously.

[0004] A minimally invasive distraction and support device would havesignificant application in orthopaedic surgical procedures, includingacute and elective procedures to treat bone fractures and degenerativechanges of the skeletal system and including vertebral compressionfractures, interbody fusion, vertebral disc augmentation or replacement,and other compression fractures including, but not limited to tibialplateau compression fractures, calcaneous compression fractures, distaltibia fractures, distal radius (wrist) fractures, crushed or fracturedorbit and orthopaedic oncology. Further, a minimally invasivedistraction and support device would have application in non-orthopaedicsurgical procedures in plastic surgery (for example facialreconstruction), gastrointestinal surgery and urological surgery (forexample the treatment of incontinence).

[0005] Vertebral Compression Fractures

[0006] A vertebral compression fracture is a crushing injury to one ormore vertebrae. Vertebral fractures are generally associated withosteoporosis (the “brittle bone” disease), metastasis, and/or trauma.Osteoporosis reduces bone density, thereby weakening bones andpredisposing them to fracture.

[0007] The osteoporosis-weakened bones can collapse during normalactivity. In severe cases of osteoporosis, actions as simple as bendingforward can be enough to cause a vertebral compression fracture.Vertebral compression fractures are the most common type of osteoporoticfractures according to the National Institute of Health. The mechanismof these fractures is one of flexion with axial compression where evenminor events cause damage to the weak bone. While the fractures may healwithout intervention, the crushed bone may fail to heal adequately.Moreover, if the bones are allowed to heal on their own, the spine willbe deformed to the extent the vertebrae were compressed by the fracture.Spinal deformity may lead to breathing and gastrointestinalcomplications, and adverse loading of adjacent vertebrae.

[0008] Vertebral fractures happen most frequently at the thoracolumbarjunction, with a relatively normal distribution of fractures around thispoint. Vertebral fractures can permanently alter the shape and strengthof the spine. Commonly, they cause loss of height and a humped back.This disorder (called kyphosis or “dowager's hump”) is an exaggerationof the spinal curve that causes the shoulders to slump forward and thetop of the back to look enlarged and humped. In severe cases, the body'scenter of mass is moved further away from the spine resulting inincreased bending moment on the spine and increased loading ofindividual vertebrae.

[0009] Another contributing factor to vertebral fractures is metastaticdisease. When cancer cells spread to the spine, the cancer may causedestruction of part of the vertebra, weakening and predisposing the boneto fracture.

[0010] Osteoporosis and metastatic disease are common root causesleading to vertebral fractures, but trauma to healthy vertebrae alsocauses minor to severe fractures. Such trauma may result from a fall, aforceful jump, a car accident, or any event that stresses the spine pastits breaking point. The resulting fractures typically are compressionfractures or burst fractures.

[0011] Vertebral fractures can occur without pain. However, they oftencause a severe “band-like” pain that radiates from the spine around bothsides of the body. It is commonly believed that the source of acute painin compression fractures is the result of instability at the fracturesite, allowing motion that irritates nerves in and around the vertebrae.

[0012] Until recently, treatment of vertebral compression fractures hasconsisted of conservative measures including rest, analgesics, dietary,and medical regimens to restore bone density or prevent further boneloss, avoidance of injury, and bracing. Unfortunately, the typicalpatient is an elderly person who generally does not tolerate extendedbed rest well. As a result, minimally invasive surgical methods fortreating vertebral compression fractures have recently been introducedand are gaining popularity.

[0013] One technique used to treat vertebral compression fractures isinjection of bone filler into the fractured vertebral body. Thisprocedure is commonly referred to as percutaneous vertebroplasty.Vertebroplasty involves injecting bone filler (for example, bone cement)into the collapsed vertebra to stabilize and strengthen the crushedbone.

[0014] In vertebroplasty, physicians typically use one of two surgicalapproaches to access thoracic and lumbar vertebral bodies:transpedicular or extrapedicular. The transpedicular approach involvesthe placement of a needle or wire through the pedicle into the vertebralbody, and the physician may choose to use either a unilateral access orbilateral transpedicular approach. The second approach, theextrapedicular technique, involves an entry point through theposterolateral corner of the vertebral body. The needle entry point istypically 8 cm to 12 cm lateral of the mid-sagittal plane, with the skinincision typically closer to 8 cm in the proximal spine and generallycloser to 12 cm in the distal spine. In general, one cannula is placedto fill the vertebral body with the extra-pedicular approach.

[0015] Regardless of the surgical approach, the physician generallyplaces a small diameter guide wire or needle along the path intended forthe bone filler delivery needle. The guide wire is advanced into thevertebral body under fluoroscopic guidance to the delivery point withinthe vertebrae. The access channel into the vertebra may be enlarged toaccommodate the delivery tube. In some cases, the delivery tube isplaced directly and forms its own opening. In other cases, an accesscannula is placed over the guide wire and advanced into the vertebralbody. After placement, the cannula is replaced with the delivery tube,which is passed over the guide pin. In both cases, a hollow needle orsimilar tube is placed into the vertebral body and used to deliver thebone filler into the vertebra.

[0016] In this procedure, lower viscosities and higher pressures tend todisperse the bone filler throughout the vertebral body. However, suchconditions dramatically increase the risk of bone filler extravasationfrom the vertebral body. The transpedicular approach requires use of arelatively small needle (generally 11 gauge or smaller). In contrast,the extrapedicular approach provides sufficient room to accommodate alarger needle (up to 6 mm internal diameter in the lumbar region andlower thoracic regions). In general, the small diameter needle requiredfor a transpedicular approach necessitates injecting the bone filler ina more liquid (less viscous) state. Further, the pressure required toflow bone filler through a small gauge needle is relatively high. Thedifficulty of controlling or stopping bone filler flow into injurysensitive areas increases as the required pressure increases. The largerneedle used in the extrapedicular approach allows injection of bonefiller in a thicker, more controllable viscous state. Therefore, manyphysicians now advocate the extrapedicular approach so that the bonefiller may be delivered through a larger cannula under lower pressure.

[0017] Caution must be taken to prevent extravasation, with the greatestattention given to preventing posterior extravasation because it maycause spinal cord trauma. Physicians typically use fluoroscopic imagingto monitor bone filler propagation and to avoid flow into areas ofcritical concern. If a foraminal leak results, the patient may requiresurgical decompression and/or suffer paralysis.

[0018] Kyphoplasty is a modified vertebral fracture treatment that usesone or two balloons, similar to angioplasty balloons, to attempt toreduce the fracture and restore vertebral height prior to injecting thebone filler. Two balloons are typically introduced into the vertebra viabilateral transpedicular cannulae. The balloons are inflated to reducethe fracture. After the balloon(s) is deflated and removed, leaving arelatively empty cavity, bone cement is injected into the vertebra. Intheory, inflation of the balloons restores vertebral height. However, itis difficult to consistently attain meaningful height restoration. Itappears the inconsistent results are due, in part, to the manner inwhich the balloon expands in a compressible media and the structuralorientation of the trabecular bone within the vertebra.

[0019] Tibial Plateau Compression Fractures

[0020] A tibial plateau fracture is a crushing injury to one or both ofthe tibial condyles resulting in a depression in the articular surfaceof the condyle. In conjunction with the compression fracture, there maybe a splitting fracture of the tibial plateau. Appropriate treatment forcompression fractures depends on the severity of the fracture. Minimallydisplaced compression fractures may be stabilized in a cast or bracewithout surgical intervention. More severely displaced compression withor without displacement fractures are treated via open reduction andinternal fixation.

[0021] Typically, the underside of the compression fracture is accessedeither through a window cut (a relatively small resection) into the sideof the tibia or by opening or displacing a splitting fracture. A boneelevator is then used to reduce the fracture and align the articularsurface of the tibial condyle. A fluoroscope or arthroscope may be usedto visualize and confirm the reduction. Bone filler is placed into thecavity under the reduced compression fracture to maintain the reduction.If a window was cut into the side of the tibia, the window is packedwith graft material and may be secured with a bone plate. If a splittingfracture was opened to gain access, then the fracture is reduced and maybe stabilized with bone screws, bone plate and screws, or a buttressplate and screws. (Both of these methods are very invasive and requireextensive rehabilitation.)

[0022] Spinal Interbody Fusion

[0023] Spinal fusion is most frequently indicated to treat chronic backpain associated with instability or degenerative disc disease that hasnot responded to less invasive treatments. Fusion is also prescribed totreat trauma and congenital deformities. Spinal fusion involves removalof the spinal disc and fusing or joining the two adjacent vertebrae. Theprimary objective for patients suffering from instability is to diminishthe patient's pain by reducing spinal motion.

[0024] Spinal fusions are generally categorized into two large groups:instrumented and non-instrumented. In non-instrumented procedures, thephysician removes tissue from the unstable disc space and fills it withsome form of bone graft that facilitates the fusion of the two adjacentvertebral bodies. Instrumented procedures are similar tonon-instrumented procedures, except that implants (generally metallic)are also applied to further stabilize the vertebrae and improve thelikelihood of fusion.

[0025] Conventional instrumented procedures generally utilize plates,rods, hooks, and/or pedicle screws through various surgical approaches.These conventional implants are secured to the vertebral bodies that arebeing fused. Interbody fusion devices were introduced in the 1990's as aless invasive surgical alternative, although interbody devices areincreasingly being used in conjunction with pedicle screws. Interbodydevices are implanted into the disc space to restore the normal discspacing, utilizing tension in the annulus to stabilize the fusion unit.Interbody fusion provides a large area of the vertebral end plate forestablishing bony fusion, a viable blood supply from the decorticatedend plates, and dynamic compressive loading of the graft site. Theinterbody devices are generally filled with a bone filler to facilitatefusion. Interbody devices can be categorized in three primary groups:spinal fusion cages, which are available in a variety of shapesincluding rectangular, round-faced, and lordotic; allograft bone dowelsand wedges (which are also available in various shapes); and titaniummesh (although titanium mesh is not itself a structural spacer).

[0026] Interbody fusion is typically completed through a posterior, ananterior, or a lateral intertransverse approach. Each of thesetechniques has limitations. Lumbar interbody fusion presents achallenging surgical procedure and relatively high pseudoarthrosisrates. As a result, this approach is increasingly combined withadditional internal fixation devices such as pedicle screw fixation.

[0027] In all interbody surgical approaches, a relatively large openingis made in the annulus. The nuclear material is removed and the endplates are decorticated to facilitate bony fusion. Overall, the use ofinterbody devices has resulted in mixed clinical outcomes. Placement ofa fixed height device presents challenges in proper tensioning of theannulus. For these and other reasons, there is concern over long-termstability of interbody devices and fusion mass.

SUMMARY OF THE INVENTION

[0028] The invention provides a combination of a temporary or long termimplantable device and instrumentation to place the device, in whichtissue surfaces are distracted along an axis to enable access to thespace between the tissues. Generally, the invention provides wafers forstacking upon one another to provide an axially extending column todistract and support tissue surfaces. While a primary use of theinvention is to reduce and stabilize vertebral compression fractures,the invention may be used in any situation where it is desirable todistract two tissue surfaces. The tissue may be bone, skin, soft tissue,or combinations thereof. Further, the surfaces may be opposed surfacesof contiguous elements or surfaces of opposed elements. Thus, theinvention may be used to treat vertebral compression fractures, forreplacement of vertebral discs, as an interbody fusion device, wedgeopening high tibial osteotomy, tibial tuberosity elevation, as well asfor treating other compression fractures including, but not limited totibia plateau fractures, calcaneous, distal tibial fractures, or distalradius (wrist) fractures. The invention may also be used for restoringthe floor of the orbit, for elevating soft tissue in cosmeticapplications, or in incontinence applications as a urethral restrictor.Alternately, the invention may be used in similar veterinaryapplications.

[0029] The Distraction Device

[0030] The terms “vertical”, “up”, etc., are occasionally used hereinfor ease of understanding, and these terms should be taken in referenceto the vertebrae of a standing patient. Thus, “vertical” refersgenerally to the axis of the spine. We may also utilize mutuallyperpendicular “X”, “Y” and “Z” axes to describe configurations andmovement, with the Z-axis being the axis of the column of wafers, thatis, the direction in which this column grows as wafers are addedsequentially to it. The X-axis refers to the axis extending generally inthe direction of movement of each wafer as it is advanced to a positionbeneath a preceding wafer, and the Y-axis is perpendicular to both theX- and Z-axes. The wafers are sometimes described with reference topermitted degrees of freedom or restraint when they are placed in acolumn. It should be understood that these permitted degrees of freedomor restraint refer to the permitted or restrained movement of one waferwith respect to an adjacent wafer along one or more of the three axes,and the permitted or restrained rotation between adjacent wafers aboutone or more of these axes.

[0031] The distraction device includes a plurality of stackable wafersdesigned for insertion between tissue surfaces to form a column. Thewafer column is assembled in vivo to provide a distraction force as wellas support and stabilization of the distracted tissue. Preferably, thewafers place distraction force in one direction only and thus providedirectional distraction. The distraction device may be permanentlyimplanted, in which case the wafer column may be used alone or inconjunction with a bone filler material. Alternately, the distractiondevice may be used temporarily to manipulate tissues and then removed.

[0032] In use, the wafers are preferably stacked between two tissuesurfaces as they are implanted, thereby distracting and supporting thetissue surfaces simultaneously. In the vertebral compression fractureapplication, it is preferable to distract along the Z-axis (along theaxis of the spine) to restore vertebral height. However, in otherapplications, it may be preferable to provide distraction in a differentdirection. The features of a wafer and a column of wafers will bedescribed relative to position and direction. The top of a wafer or thetop of the column is defined as the face of the wafer or column in thedirection of distraction. The bottom of a wafer or the bottom of thecolumn is defined as the face opposite the top face. In similar fashion,above and below a wafer or column implies along the top and bottom ofthe wafer or column, respectively. Each wafer has a leading edge thatenters the forming column first and a trailing edge opposite the leadingedge. The sides of the wafer are adjacent the leading and trailing edgesand the top and bottom faces of the wafer. In general, the sides arelonger than the leading and trailing edges, however the sides may beshorter than the leading and trailing edges. The axis of the column isdefined as a line parallel to the direction of distraction.

[0033] During implantation, the wafers are stacked to form a column tosimultaneously distract and support the two tissue surfaces. Theinvention provides that trailing wafers can be positioned above or belowthe leading wafers to form a column. In one embodiment, the wafers aredesigned to be beveled at both their leading and trailing edges so thatwhen lined up end-to-end, force on the trailing edge of the trailingwafer causes its leading edge to slide below the trailing edge of theleading wafer, thereby lifting up the leading wafer. Likewise, the bevelof the leading and trailing edges may be reversed enabling insertion ofa trailing wafer above a leading wafer. Alternately, the leading andtrailing edges may be chevron shaped or curved when viewed from theside, enabling insertion of trailing wafers between any two leadingwafers or on the top or bottom of the column. In another embodiment, thewafers may be configured with blunt edges wherein the wafers are stackedwith the insertion instrument. In all embodiments, by repeating theprocess with consecutive wafers, the column height increases to restorevertebral height.

[0034] The specific configuration of each wafer may be altered to bettersuit the application for which the wafer will be used. For instance, thethickness of the wafer and the angle of the bevel may be varied toprovide a mechanical advantage and insertion force within acceptableranges for a given application. A more acute bevel angle will providegreater vertical force for a given insertion force. In addition, waferthickness may be varied to increase or decrease resolution available tothe physician in performing a given surgical procedure. A thinner waferwill provide greater displacement resolution and incremental forcegeneration to the physician in performing the procedure. A variation ofwafer thicknesses may be used in combination to form a column andmultiple wafers may be inserted into the column simultaneously. The topand bottom faces of a wafer may be parallel or oblique to enablebuilding a column that is straight or curved, respectively. Parallel oroblique-faced wafers may be used independently or in combination tobuild a column that has straight and/or curved sections.

[0035] In order to place the wafers between the tissue surfaces, a waferinserter is positioned within the surgical site with access at itsdistal tip to the tissue surfaces to be distracted and supported. Awafer is placed on the track and a plunger is used to advance the waferto the distal end of the track. This is repeated with consecutive wafersuntil a column of sufficient height is created per physician discretion.After the wafer(s) have been inserted, the insertion device is removed.The distal end of the insertion device may be manufactured from the samematerial as the wafers and/or be detachable. In this embodiment, thedistal end of the insertion instrument would be detached after placingthe wafer column, and the instrument removed.

[0036] Optionally, bone filler may be injected into the vertebra tofurther stabilize the distracted tissues. The first wafer inserted maybe longer and/or wider than subsequent wafers. The size differential mayfacilitate bone filler flow around the wafers. In addition, the waferscan be designed with various tunnels, grooves, and/or holes to improvewafer encapsulation, bonding between the wafers and any injected bonefiller, and to provide a pathway for bone filler to penetrate the wafercolumn.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 shows a vertebral body having a compression fracturedisplacing its superior and anterior edge.

[0038]FIG. 2 shows a vertebral body, following treatment of acompression fracture.

[0039]FIG. 3 illustrates a plan view of a distraction device insertionapparatus according to an embodiment of the invention, placed within avertebral body shown in cross-section.

[0040]FIG. 4 illustrates a cross-sectional view of the insertionapparatus of FIG. 3 deploying a distraction device according to anembodiment of the present invention.

[0041]FIG. 5 illustrates a cross-sectional view of the insertionapparatus of FIG. 4 deploying a distraction device according to analternate embodiment of the present invention.

[0042]FIG. 6 shows a plan view of a configuration of distraction deviceaccording to one embodiment of the present invention.

[0043]FIG. 7 shows an alternate plan view of the distraction deviceconfiguration of FIG. 6.

[0044]FIG. 8 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

[0045]FIG. 9 shows an alternate plan view of the distraction deviceconfiguration of FIG. 8.

[0046]FIG. 10 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

[0047]FIG. 11 shows an alternate plan view of the distraction deviceconfiguration of FIG. 10.

[0048]FIG. 12 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

[0049]FIG. 13 shows a sectional view of the distraction deviceconfiguration of FIG. 12.

[0050]FIG. 14 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

[0051]FIG. 15 shows a sectional view of the distraction deviceconfiguration of FIG. 14.

[0052]FIG. 16 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

[0053]FIG. 17 shows an alternate plan view of the distraction deviceconfiguration of FIG. 16.

[0054]FIG. 18 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

[0055]FIG. 19 shows an alternate plan view of the distraction deviceconfiguration of FIG. 18.

[0056]FIG. 20 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

[0057]FIG. 21 shows an alternate plan view of the distraction deviceconfiguration of FIG. 20.

[0058]FIG. 22 shows a plan view of a configuration of distraction deviceaccording to an alternate embodiment of the present invention.

[0059]FIG. 23 shows an alternate plan view of the distraction deviceconfiguration of FIG. 10.

[0060]FIG. 24 shows a plan view of a distraction device according to analternate embodiment of the present invention.

[0061]FIG. 25 shows a plan view of a configuration of several of thedistraction device of FIG. 24.

[0062]FIG. 26 shows an alternate plan view of the configuration of thedistraction device of FIG. 25.

[0063]FIG. 27 shows a plan view of a configuration of distraction devicedeployed within a vertebral body, shown in sectional view.

[0064]FIG. 28 shows a plan view of a further configuration ofdistraction device being deployed within a vertebral body, shown insectional view.

[0065]FIG. 29 show a sectional view of a portion of an insertion deviceaccording to one embodiment of the present invention.

[0066]FIG. 30 shows a sectional view of an entire insertion device, asection of which is depicted in FIG. 29.

[0067]FIG. 31 show a plan view of a series of undeployed distractiondevices connected by a tether according to one embodiment of the presentinvention.

[0068]FIG. 32 shows a plan view of an alternate state of the distractiondevices of FIG. 31.

[0069]FIG. 33 shows a plan view of an alternate state of the distractiondevices of FIG. 31.

[0070]FIG. 34 shows a sectional view of an insertion device according toone embodiment of the present invention.

[0071]FIG. 35 shows a sectional view of a portion of the insertiondevice of FIG. 34.

[0072]FIG. 36 shows a sectional view of a portion of the insertiondevice of FIG. 35.

[0073]FIG. 37 shows a sectional view of a portion of an insertion deviceaccording to an alternate embodiment of the present invention.

[0074]FIG. 38 shows a plan view of an alternate state of the insertiondevice of FIG. 37.

[0075]FIG. 39 shows a sectional view of an insertion device according toan embodiment of the present invention, configured to deploy distractiondevice similar to that depicted in FIGS. 31-33.

[0076]FIG. 40 shows a sectional view of an alternate state of theinsertion device depicted in FIG. 39, configured for the removal of thedistraction device similar to that depicted in FIGS. 31-33.

[0077] FIGS. 41-45 show sectional views of an embodiment of an insertiondevice according to the present invention, with corresponding suitabledistraction device, in various states attendant to clinical deployment.

[0078]FIG. 46 shows a plan view of a clinical deployment deviceaccording to an alternate embodiment of the present invention, insertedinto a vertebral body, shown in cross-section.

[0079]FIG. 47 depicts the implementation of a regimen for treatment of avertebral compression according to an embodiment of the presentinvention, by plan view.

[0080]FIG. 48 depicts the implementation of a regimen for treatment of avertebral compression according to an alternate embodiment of thepresent invention.

[0081]FIG. 49 shows a plan view of an apparatus for use in deploying thedistraction device according to a further alternate embodiment of thepresent invention.

[0082]FIG. 50 shows a plan view of an apparatus for use in deploying thedistraction device to be used in conjunction with the apparatus of FIG.49.

[0083]FIG. 51 shows a plan view of an apparatus according to anembodiment of the present invention.

[0084]FIG. 52 shows an alternate plan view of the apparatus of FIG. 51.

[0085]FIG. 53 shows a plan view of the apparatus of FIG. 52 according toan alternate state.

[0086]FIG. 54 shows a plan view of an apparatus according to anembodiment of the present invention.

[0087]FIG. 55 shows a plan view of an alternate embodiment of theapparatus depicted in FIG. 54.

[0088]FIG. 56 shows a sectional view of an apparatus according to anembodiment of the present invention, suitable for deployment ofdistraction device similar to that depicted in FIGS. 31-33.

[0089]FIG. 57 shows a sectional view of an alternate configuration ofthe apparatus depicted in FIG. 56.

[0090]FIG. 58 shows a plan view of a bone filler insertion toolaccording to one embodiment of the present invention.

[0091]FIG. 59 shows a sectional view of the bone filler insertion tooldepicted in FIG. 58.

[0092]FIG. 60 depicts the implementation of a regimen for treatment of avertebral body according to an embodiment of the present invention.

[0093]FIG. 61 depicts the deployment of an insertion device according toan embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0094] The invention provides a combination of an implantabledistraction device and instrumentation to place the device. Thedistraction device is detailed in this section by its application to thevertebral compression fracture. FIG. 1 shows a vertebral body 60 havinga compression fracture displacing its superior and anterior edge 62.FIG. 2 shows a vertebral body 60 wherein the height has been restored.

[0095] The Distraction Device

[0096] A plurality of stackable wafers is provided for insertion betweentwo tissues and is delivered to a surgical site along an axis transverseto the axis of distraction. Multiple wafer insertions result in a columnof wafers at the surgical site that simultaneously distracts andsupports the two tissues.

[0097] The wafers may be formed from a solid form of bone fillermaterial, and/or any other suitable material such as but not limited toimplantable grade alloys (including, but not limited to titanium, cobaltchrome, nitinol, or stainless steel), other medical grade composites(including, but not limited to polyetheretherketone polymer (PEEK),ultra-high molecular weight polyethylene, or polyethylene) otherceramics (including, but not limited to zirconia, alumina, orcalcium-phosphate based ceramics), and resorbable polymers (for example,polylactic acid (PLA), polyglycolic acid (PGA), andpoly(lactide-coglycolide) (PLGA)). The wafers may be dense or porous,while porous wafers may be filled with resorbable polymers to increasemechanical strength. For soft tissue applications, it may be desirableto manufacture the wafers of woven collagen pads, tissue engineeredmaterials, chitin, urethanes, silicone, or silicone materials.Alternately, the wafers may be manufactured from hydrogel (polyvinylalcohol) in which the wafer is inserted in a dehydrated form and expandswith fluids present at the insertion site. Hydrogel wafers may beparticularly desirable for placing in the disc space between vertebrae.For purposes of this disclosure, these materials and their combinationswill be collectively defined as the “implant materials.” Further, thewafers and implant materials may be combined with osteoinductive agents(including BMPs, growth factors, cell therapy, gene therapy, and patientderived factors) and other drug therapies. The osteoinductive agents maybe added to initiate and accelerate bone formation while the drugtherapies may range from antibiotics to reduce the risk of infection tochemotherapy to treat cancer. Optionally, the wafers may be used with aflowable bone filler material. For the purposes of this disclosure, bonefiller is defined as any substance used to stabilize the bone andincludes, but is not limited to bone cement (polymethyl methacrylatePMMA, or PMA), other composite material, human bone graft (allograft orautograft), synthetic and xenograft derived bone substitutes (calciumphosphate, hydroxylapatite, and/or other ceramic based bonesubstitutes), collagen, or combinations of these materials.

[0098] The invention provides that the wafer column is formed in vivo byusing a wafer inserter. FIG. 3 illustrates a wafer inserter 64 placedwithin a vertebral body with a wafer 66 positioned distally on the waferinserter 64. During implantation, the wafers are stacked to form acolumn to restore vertebral height. FIGS. 25 and 26 show a wafer column192 supporting the proximal end plate of a vertebral body.

[0099] Consecutive wafer insertions result in a column of wafers at thesurgical site. In one embodiment, the trailing edge of a wafer isbeveled or otherwise configured to guide the next wafer under the first.FIG. 4 illustrates a wafer 70 being inserted under a preceding wafer 72.The leading edge 74 of the wafer is beveled to guide it under the onethe trailing edge 76 of the preceding wafer, which is correspondinglybeveled to guide the subsequent wafer underneath. Chevron and roundededges may be used in the same manner as beveled edges to guide theleading edge of one wafer under the trailing edge of another.Alternately, the wafer edges may be squared and the tool for insertingthe wafers may be used to lift the trailing end of the leading wafer andslide the trailing wafer thereunder as depicted in FIGS. 41-45.Similarly, any configuration of wafer or tool may be used to allow thewafers to stack into a column during insertion into the body.

[0100] The wafer design may be varied to suit the requirements ofspecific surgical applications. Wafer thickness may range from 0.2 mm to6 mm, and bevel angle (the angle between the leading and trailing facesof a wafer and the direction of insertion) may range from 2 to 90degrees. The mechanical advantage and the insertion force may bedesigned within acceptable ranges for a given application by varying thethickness and the bevel angle. A more acute bevel angle will providegreater vertical force for a given insertion force. In addition, waferthickness may be varied to increase or decrease displacement resolutionfor a given surgical procedure. A thinner wafer will provide greaterdisplacement resolution and incremental force generation.

[0101] Specifically for vertebral compression fracture applications,exemplary wafer dimensions range as follows:

[0102] Wafer length between 5 mm and 40 mm;

[0103] Wafer width between 2 mm and 16 mm;

[0104] Wafer thickness between 0.2 mm and 6 mm; and

[0105] Curved wafer radii between 10 mm and 500 mm.

[0106] These dimensions are provided only as guidelines and any suitabledimensions may be used. Furthermore, the dimensions of the wafer willlikely vary widely when the wafers are used in other applications, suchas, for example, treating tibial plateau fractures.

[0107] The wafers may be rigid, as seen in FIG. 4, or may be flexible,as seen in FIG. 5. A rigid wafer may tend to pivot over the leading edgeof the subsequent wafer as it is inserted, placing a bending moment onthe wafer. A flexible wafer 80 tends to conform to the leading edge ofthe subsequent wafer as it is inserted. The stiffness of the wafer willbe dependent on the material selected and the cross sectional geometryof the wafer. When stiffer materials are selected, the wafer thicknessand bevel angle may be optimized to minimize the bending moment placedon the preceding wafer or wafers.

[0108] In addition, the wafer thickness may be uniform or varied.Specifically, the wafers may be either flat or wedged, or alternativelyinclude a combination of flat and wedged wafers. The wedge may increasein thickness from leading edge to trailing edge or vice versa, or mayincrease in thickness from side to side. The wedged wafers may be ofvarious angles. For example, the physician reducing a compressionfracture may observe that the column is not parallel to the end plate.As the end plate is returning to its anatomical position, anappropriately wedged wafer(s) may be inserted to gradually curve thecolumn to provide a parallel interface with the end plate. Similarly,the wafers may be wedge shaped with the anterior aspect of the waferthicker than the posterior aspect to reproduce the natural lordoticcurvature of the spine for interbody fusion. In addition, wafers ofdifferent thickness may be inserted into the same column.

[0109] A further option is to alter the interface of one wafer to apreceding or following wafer to suit a specific application. Theinterface may provide various degrees of freedom to accommodate varioussurgical applications. These include unconstrained, semi-constrained inselect degrees of freedom, and totally constrained applications.Changing the wafer's surface configurations often varies the waferinterfaces. The surface configurations may be applied independently orin combination, based on the demands of the surgical application.

[0110] For example, if the wafers are to be implanted in a fashion thatdoes not require alignment of one wafer to the next wafer, theinterfaces between the wafers may be generally flat. This configurationprovides a simple unconstrained wafer interface. The generally flatcontact faces allow the wafers to translate relative to one another inthe plane of the interface. They are also free to rotate about an axisnormal to the interfaces. Optionally, the wafers may be distracted fromone another.

[0111] An unconstrained wafer configuration is shown in FIG. 6 where thewafers 86 are flat wafers with no surface texture, that is, withsurfaces that may rigidly slide on one another. These wafers are limitedin compression along the Z-axis and rotation about the X- and Y-axes.However, distraction along the Z-axis is free. Translation and rotationare permitted along the X- and Y-axes in the plane of the interface.FIG. 7 provides an end view of the flat wafer 86 configuration.

[0112] On the other hand, if a semi-constrained wafer interface isdesired, the wafers may be otherwise configured. For example, if thewafers are designed for placement in a vertical column wherein they areallowed to slide longitudinally, then the interfaces between the wafersmay have a longitudinal groove 88 to align the wafers as shown in FIGS.8 and 9. FIGS. 8-11 illustrate a preferred wafer embodiment. The wafers90 have beveled leading edges 92 and beveled trailing edges 94 tofacilitate sliding of a subsequently inserted wafer under the leadingwafer. As seen in FIGS. 8 and 9, the wafers 92 include ridges 96 alongtheir bottom surfaces and corresponding grooves 98 along their topsurfaces to limit motion of one wafer to another. Similarly, the ridgemay be located along the top wafer surface and the groove located on thebottom surface, as shown in FIGS. 10 and 11.

[0113] As shown in FIGS. 12-15, the wafer may have a “lip” built intothe undersurface 100 and corresponding ridge 102 on the top surface ofthe subsequent wafer to limit axial travel of the subsequent wafer alongthe X-axis or Y-axis as desired. The undersurface 100 is the surface ofthe wafer adjacent to the insertion track. The lip 104 can extend alongthe leading edge of the wafer (preventing translation along the X-axis)as seen in FIGS. 12 and 13, or the lip can extend along the lateral (notleading or trailing) edges of the wafer (preventing translation alongthe Y-axis), or as shown in FIGS. 14 and 15, the lip 106 can extendalong the lateral edges and the leading edge (preventing translationalong the X- and Y-axes). However, the lip should not extend along thetrailing edge of the wafer as such a configuration may interfere withthe interface between the wafer and the subsequent wafer. Furthermore,FIGS. 16 and 17 illustrate the lip in a tapered configuration 108 with amechanical detent 110 along the length of the taper. A correspondingtapered ridge 112 along top of the subsequent wafer engages the taperedlip 108. Similarly, the mechanical detents 114 on the tapered ridge 112engage the corresponding mechanical detents 110 in the tapered lip 108.The tapered lip may be configured without mechanical detents wherein thetaper angle would be such to promote a frictional lock between thewafers when axially loaded. Alternatively, the groove may be a dovetailto provide longitudinal sliding and a vertical lock between the wafers.

[0114] Another wafer embodiment, shown in FIGS. 18 and 19, involveswafers 120 having cylindrical (arched surface) interfaces. The axis ofthe cylinder is along the X-axis of the wafer, allowing adjacent wafersto slide along an arch about the X-axis. Such motion enables the top andthe bottom of the column to conform to non-parallel tissue supportsurfaces while applying a distraction force to the tissue surfaces. Thewafers are restricted in translation in the Y-axis and rotation aboutthe Z-axis. If desired, the top 122 and bottom 124 wafers of acylindrical column may have flat top 126 and bottom 128 surfacesrespectively, as seen in FIGS. 20 and 21, to facilitate uniform supportby tissue support structures.

[0115]FIGS. 22 and 23 show an alternate wafer design providingsemi-constrained wafer interfaces 130. The wafers have spherical (or,optionally, hemispherical or less than hemispherical) interfaces thatprovide rotation about all three-principle axes. In this embodiment,translation along the X- and Y-axes and compression along the Z-axis arerestricted. Distraction along the Z-axis and rotation about the Z-, Y-,and X-axes are free. Optionally, the top and bottom wafers may be flat(not shown) on their top 132 and bottom 134 surfaces respectively. Ifflat, the top 132 and bottom 134 surfaces facilitate uniform supportfrom support structures.

[0116] In another embodiment, the semi-constrained wafer interfaces maybe pinned to one another allowing rotation in the plane of the interfaceabout a fixed axis.

[0117] In yet another embodiment of semi-constrained wafer interface,the wafer interfaces may be keyed together to prevent distraction of thewafers. Such keyed interfaces may include but are not limited to adovetail (see for example FIG. 24), “T” bolt, or key hole design thatallows the wafers to translate along the axis of the keyed elements.Translation normal to the keyed elements, distraction, and rotation arerestricted.

[0118] Another option is to constrain the wafer interfaces. In one suchembodiment, the wafer interface includes a combination of a keyedelement and a snap-in pin that can be used to allow sliding one waferonto another to provide lifting force. The keyed elements providerestriction of translation normal to the keyed element and distractionand rotation. The addition of a pinned element that snaps in placeprovides restriction of translation along the axis of the keyed element.

[0119] FIGS. 24-26 show a wafer configuration combining a dovetail 140and a cylindrical indent 142. This limits compression and distractionalong the Z-axis, translation along the X- and Y-axes and rotation aboutthe X-, Y-, and Z-axes. Thus, the wafers are constrained in all degreesof freedom.

[0120] Alternately, a constrained wafer interface may include a series(two or more) of pressfit pinned interlocks that engage when one waferis properly positioned above another and the two wafers are compressedtogether.

[0121] If the wafers are intended for stacking in a vertical column withtranslation locked, the wafer interfaces may be keyed together with aboss on each wafer that fits into a mating cavity on an adjacent wafer.The boss may be of any suitable shape, such as cylindrical or square.Further, if vertical locking is needed, the boss feature may be combinedwith a dovetail or other keyed mechanism to lock the wafers fromvertical separation.

[0122] A further wafer option is to alter the shape of the wafers. Thewafers may be straight or may be curved along a constant radiusextending from an axis parallel to the axis of the desired wafer column.In the case of straight wafers, stacking is longitudinal and theinsertion instrument deploys the wafers linearly. In the case of curvedwafers, stacking is along the arch of the curve and the insertioninstrument deploys the wafers along an arch. Reference is made to FIG.46. Alternatively, the curved wafers may have a ridge on the top surfaceof slightly different configuration than that of the mating groove onthe under surface thereby creating a frictional lock when one wafer isinserted under another. In all wafer embodiments containing matingridges and grooves, the ridges are described as being on the top surfaceof the wafer and the groove on the bottom surface. The wafers wouldfunction equivalently if the groove were on the top surface and theridge on the bottom surface.

[0123] In certain applications, it may be beneficial for the wafers tobe secured to one another after insertion. Any suitable method forsecuring the wafers to one another as known by those skilled in the artsmay be used. Wafers may be secured to one another by means of anadhesive bond, a chemical bond, and/or a mechanical interlock (asdescribed above). Applying a generic fluent adhesive, for examplecyanoacrylate, into the cavity surrounding the column provides adhesivebonding. The fluent adhesive hardens and locks the wafers.

[0124] Introducing a liquid material that is chemically equivalent tothe wafer provides a potential chemical bonding. For example, the wafersmay be manufactured from bone cement and bone cement may be injectedaround the wafers and into the vertebral body. The monomer in the bonecement may initiate a chemical bonding between the wafer and the bonefiller, thereby locking the wafers together. A stable construct combinedwith cement interdigitation is believed to provide stability and painrelief in a crushed vertebra.

[0125] It is also possible to enhance the wafer-to-wafer bonding and thewafer-to-bone filler bonding should bonding be desired. One method fordoing so involves solvent bonding in which the wafers are wiped with anappropriate solvent as they are inserted into the vertebra. A secondmethod involves coating the wafers with a microencapsulated solvent. Thesetting or hardening time for adhesives or solvent bonding may bedesigned to allow time to properly position the wafer column.Alternatively, the adhesives or solvents may be activated by additionalmeans such as light, heat, an activator, or other means that allowplacing and positioning the wafers before securing them to one another.

[0126] A preferred method of wiping the wafers with solvent includesequipping the wafer inserter with a reservoir of solvent. A channel andwick design transports solvent to the distal end of the wafer inserter.As the wafers are inserted, they pass over the wick coating them withsolvent. Once inside the vertebra and formed as a column, the wafersbecome bonded to each other by solvent bonding. The solvent may alsoenhance the bonding of the wafers to the bone filler that may beinjected later in the procedure.

[0127] In order to coat the wafers with a layer of micro spherescontaining solvent, the wafers are coated prior to insertion. As thewafers are passed through the wafer inserter and slide across oneanother in the column, the micro spheres are ruptured to release thesolvent. The solvent then bonds the wafers to one another and preps theouter surface to enhance bonding to the bone filler injected later.

[0128] The wafers may also include tunnels, grooves, or holes tofacilitate movement of bone filler through the wafer column into thesurrounding bone. Further, openings may be provided through the wafersto allow communication between the tunnels, grooves, or holes oradjacent wafers. In any configuration, bone filler material injectedinto the wafer column would then flow through the column, fullyencapsulating the wafers and better bonding the wafers to the bonefiller.

[0129] A preferred wafer embodiment includes radiopacity to enablevisualization. For example, a radiopaque material such as a metal markeror barium sulfate may be combined with the wafer material when thewafers are manufactured. Injection molding of the wafers with an x-raymarker inside the wafer, machining the wafers with a pressfit hole foran x-ray marker, applying a layer of radiopaque epoxy, or bonding aradiopaque marker onto the surface of the wafer are other non-limitingexamples of inclusion of radiopaque materials. Alternatively, the firstand last wafers may be made of a suitable radiopaque material, such asmetallic or plastic, to enable visualization of the top and bottom ofthe forming wafer column under fluoroscopy.

[0130] In a clinical application, the wafers are inserted such thatconsecutive wafer insertions form a column. FIG. 27 illustrates a column192 formed of equally sized wafers 194 inserted through wafer insertertrack 196. However, in some situations it may be desirable to configurethe top 198 and bottom 200 wafers of the column 192 larger than theintermediate wafers 202 as shown in FIG. 28. The larger top and bottomwafers will provide larger surface area over which to distribute loads.As the larger, first wafer is elevated, a space is created between theedges of the subsequent wafers and the surrounding tissue. This spacewould be equivalent to the overhang of the first wafer. The final wafer,or alternatively, the detachable distal end of the inserter, may also belarger than intermediate wafers 108 so as to create an overhang similarto that of the first wafer while also increasing the contact area. Theend result is a channel around the interspaced wafers through which thebone filler may flow to fully encapsulate the wafers and tointerdigitate with surrounding tissue 204.

[0131] It may be advantageous to form multiple wafer columns extendingaxially in opposite directions. This can be done by a variety ofdifferent methods. One method involves using multiple wafer inserters.For example, if two opposing wafer columns are to be formed, then onewafer inserter is deployed to form a wafer column directed superiorly,while a second wafer inserter is deployed to form a wafer columninferiorly, opposite the first column. The separate wafer inserters mayhave different access locations through the cortical wall of thevertebral body. The wafer inserters may be parallel to one another, orskewed to one another, or one may enter the vertebral body through theipsilateral cortex relative to the first wafer inserter. In addition,the wafer inserters may be adjacent one another or may be separated bycancellous bone. Alternately, as seen in FIGS. 29 and 30, a single waferinserter 40 might be used wherein the wafer inserter is able to deploywafers in opposing directions, one column deployed superiorly 212 andthe other deployed inferiorly 214. Deployment of wafers in eachdirection may be independent, in which case the physician, based onintraoperative assessment, may expand the wafer column proximally ordistally as needed. Alternatively, wafer deployment may be simultaneousin each direction, in which case a wafer would be added to the wafercolumns forming in opposing directions.

[0132] The wafers may be connected, prior to implantation, by a tether.The tether may be a thin ribbon manufactured of nitinol, suture, ribbon,or similar material. The tether may be thin and rope-like or wide andband-like. FIG. 31 shows an embodiment where the tether 218 runs alongthe top surface (224 of FIG. 32) of the wafer 220. The wafers 220 areplaced in the track 222 with the tether 218 connecting them. A side viewof the same embodiment is shown in FIG. 32. Connection via the tetherallows the wafers to be easily removed after placement. When a tether isused to connect the wafers, the wafers may also be formed with groovesor surface configurations to control translational movement.

[0133] Preferably, the wafers are molded around a tether wherein thetether is positioned at the top of the wafers to form a continuoussliding surface. The sliding surface prevents the wafers from “catching”on the wafer inserter as they are removed from the surgical site throughthe wafer inserter. The wafer is pulled up to the leading edge of thetrack and the tether provides a smooth transition as the wafer is fedinto the track during extraction. The length of the tether is slightlylonger than the length of a wafer to facilitate stacking the wafers invivo.

[0134] The wafers connected via a tether are especially useful when thewafers are used as a bone tamp. This configuration may be used insituations where it is desirable to form a space between tissues andthen remove the column. FIG. 33 shows an expanded column formed ofwafers 220 connected via a tether 218 to illustrate the path of thetether as the column is formed. An implant manufactured from any of thematerials previously described may be placed in the cavity created bythe removed column of wafers, or bone filler may simply be injected.

[0135] Further embodiments of the connected wafer configuration includeusing two tethers running along the lateral edges of the top surface ofthe wafers. The wafers and tether may alternately be integrally formedas a continuous string of wafers. In this embodiment, the string ofwafers is configured from a continuous piece of material wherein thewafers and tether are integrally formed. The tether enables stacking ofthe wafers. Yet another embodiment involves placing a wire mesh formedof small diameter wire, for example 0.001″, along the top surface of thewafers. The wire is optionally stainless steel, nitinol, or othersuitable metal or plastic or fabric. Furthermore, the wafers may bespaced and secured inside a woven tube to enable stacking of the wafersonce inserted by the wafer inserter. The wire tube is woven of a wiremesh formed of a small diameter wire, for example 0.001″ diameter. Thetube has a circumference equal to the cross-sectional circumference of awafer.

[0136] The Wafer Inserter

[0137] A wafer inserter is provided as part of the invention to deliverthe wafers to the surgical site and to form a column of wafers. In oneembodiment, the wafer inserter applies a force along the X-axis (theaxis of insertion) to a wafer that is to be added to the column. Aspreviously described, the wafers may be configured with beveled ends tofacilitate lengthening along the Z-axis of the column as the additionalwafer is inserted. In an alternate wafer embodiment also previouslydescribed, the edges of the wafers are squared and the wafer inserterraises the leading wafer to place the trailing wafer thereunder.

[0138] Numerous variations of the wafer inserter are possible, theembodiments generally including, but not limited to, a track, a plunger,and a cartridge. The wafer inserter is comprised of a track, which is along narrow channel through which wafers pass when placed into the wafercolumn. A plunger generally advances wafers down the track. Multiplewafers are housed in a cartridge of the wafer inserter for advancementdown the track. Preferably included is a mechanism for feedingsubsequent wafers into the track in front of the plunger. Further, thetrack is configured for removal from the surgical site while leaving thewafer column intact.

[0139] In a hand-held embodiment, a mechanical mechanism is provided forconverting grip strength into a force to advance the plunger. The waferinserter may include a device to measure the force applied to theplunger or along the axis of the wafer column. This device may be, forexample, a force transducer. A device, for example a counter, may alsobe included to monitor the number of wafers inserted. The total forceapplied may be thus monitored and may reference a preset adjustableforce guideline. A device to display the measured force and/or thenumber of wafers inserted may also be included. It may be desirable toprovide a mechanism to limit the force applied along the axis of thewafer column as well as means for the physician to adjust such force.Additionally, in order to inject bone filler to further stabilize thewafer column, a means to open the channel of the track to accommodatesuch bone filler may be provided.

[0140] One embodiment of the wafer inserter is illustrated in FIG. 34.The handle 230 may be gripped to position the wafer inserter 232. Thewafer inserter 232 has, at its proximal end 234, a magazine 236containing wafers 238. The wafers 238 may be stacked in the magazine 236with a top surface of one wafer supporting the bottom surface of anadjacent wafer. The handle 230 is equipped with a trigger 240 forforcing wafers out of the magazine 236. Optionally, the magazine 236 isequipped with a spring 242 to load wafers 238 along the track 244 of theinserter 232. The track 244 of the inserter 232 extends from themagazine 236 to the surgical site at its distal end 246. As they enterthe wafer track 244, the wafers 238 are aligned with the leading edge ofone wafer adjacent the trailing edge of a preceding wafer. The track 244in the embodiment shown in FIG. 34 includes a lower cavity 250 and anupper cavity 252. The plunger extends through the lower cavity 250 whilethe wafers 238 are aligned along the upper surface of the plunger. Anopening is provided along the top surface of the lower cavity 250 at thedistal end 246 of the track 244 to accommodate a wafer. Thus, as theplunger is retracted past the trailing edge of the furthest distalwafer, the wafer drops into the lower cavity. The plunger pushes thewafer distally to form a column of wafers 254. FIG. 35 provides a closeup of the wafer inserter magazine 236, track 244, and distal end 246.FIG. 36 shows an extreme close up of the distal end 246 of the waferinserter 232 along the track 244.

[0141] A wafer inserter configured for deployed wafer columns inopposite directions is depicted in FIG. 30. Two triggers, 211 and 213are included in the handle 230 and are operatively coupled to upper andlower magazines of wafers 210 and 209, respectively. The upper trigger211 inserts a wafer at the bottom of the top wafer column 212 andadvances that column superiorly (in the positive Z-axis). The bottomtrigger 213 inserts a wafer at the top of the lower wafer column andadvances that column inferiorly (in the negative Z-axis). Alternatively,the wafer inserter could be designed so that one trigger could controlboth columns independently. Other configurations for deploying opposingwafer columns with a single wafer inserter may be used as would beobvious to a person skilled in the art.

[0142] Another possible wafer inserter embodiment includes a modulardesign, including a cartridge and track detachable from the handpiece.All the components may be disposable, or alternatively reusable, or somecombination thereof. Such a design may simplify the use of multiplewafer sizes and configurations.

[0143] One method to deliver the wafers is through an inserter thatguides the wafers into position and provides the force along the X-axisto slide one wafer under another and provide the lifting force acrossthe height of the column to meet the surgical demands of the procedure.The inserter may be a fixed tip inserter but may also be a detachabletip inserter.

[0144] The fixed tip inserter provides a floor over which the wafersslide into position. The fixed tip references the distal tip of thewafer inserter track that directly supports the wafer column. A catch isdesigned at the distal end of the floor to hold the first wafer in placewhile the second wafer is inserted under the first. The second waferelevates the first wafer and begins the wafer column. The second waferis then held in place by the distal catch while the third wafer isinserted. The process is repeated until the desired column height isattained. The distal catch may engage the bottom wafer only or,optionally, may be configured to engage the bottom two or more wafers.If the sliding friction between the wafers results in an axial forcethat would advance the upper wafer while the lower wafer is inserted,having the catch engage the second wafer would prevent displacement ofthe upper wafer while building the column. However, if the friction islower than the force to advance the upper wafer (i.e. the strength ofthe surrounding cancellous bone or tissue), then a shorter catch toengage only the bottom wafer would be adequate.

[0145] In the fixed-floor embodiment of the wafer inserter, wafers areinserted until the required height or force is attained. At that point,the distal catch is released. A longer plunger (removal plunger) may beused to remove the inserter. The removal plunger is placed along thetrack of the inserter and the inserter advance mechanism is used to pushthe inserter out of the vertebral body. The removal plunger pushesagainst the bottom wafer. The bottom wafer retains its position in thecolumn within the vertebra and the reaction force forces the waferinserter out from the vertebra. Similarly, the standard plunger may bedesigned with selectable travel. The plunger may be set to insertwafers, or to advance further and remove the wafer inserter. The heightof the wafer column would be reduced by the thickness of the fixed tip,which preferably would be approximately 0.010″ to 0.020″ thick. Thedetachable tip wafer inserter embodiment, as seen in FIG. 37, includes adistal tip 260 of the wafer inserter 262 that is detachable from themain portion 264 of the inserter. One advantage provided by thedetachable tip is that the height of the wafer column is not alteredwhen the wafer inserter is removed. The tip 260 is preferablymanufactured of the same material as the wafers. Thus, in a preferredembodiment, if the wafers are manufactured of PMMA, the distal tip 260of the wafer inserter 262 is manufactured of PMMA. Alternately, thedistal tip 260 may be manufactured of an implant grade metal or othermedical grade implantable material. The distal tip 260 has a fixeddistal shoulder 266 that holds the first wafer in place while the secondwafer is inserted under the first. The height of the distal shoulder 266may provide a stop for one wafer, or it may provide a stop for two ormore wafers. The considerations applicable to the height of the distalcatch apply to the height of the distal shoulder as well.

[0146] In the detachable tip embodiment, wafers are inserted until thedesired height or force is attained. As seen in FIG. 38, the distal tip260 is then released from the main portion 264 of the wafer inserter andthe main portion 264 of the inserter is removed. The distal tip may bepressfit onto the track or may be bonded with an appropriate adhesive.In either case, the interface is designed to support the forcesgenerated while building a wafer column, but shear when the extractionplunger is used to remove the wafer inserter. Optionally, the distal tip260 may be keyed to interlock with the main portion 264 of the waferinserter. For example, the main portion of the inserter may interlockwith the distal tip by spring-loaded hooks that are mechanicallycompressed when the tip is to be released. Alternately, the hooks may bespring-loaded in the release position and mechanically expanded toengage the distal tip. In another embodiment, the detachable tip may bepressfit onto the wafer inserter or bonded with a weak adhesive. Whenthe wafer inserter is to be removed, a force may be applied using alonger plunger or equivalent mechanism as in the fixed tip waferinserter to dislodge the removable tip. The track of the wafer insertermay be then removed.

[0147] Both the fixed tip and detachable tip wafer inserters can beconfigured to deploy wafers in opposing columns. In such an embodiment,one column may be built in the positive Z-axis. Thus, if the supportingbone below the distal end of the track begins to yield, a second columnin the negative Z-axis can be built by inserting wafers below the track.Once the negative Z-axis column has provided enough support for thewafer inserter, insertion of wafers into the positive Z-axis column canbe resumed. The considerations applicable to distal stop or catch andmaterial selection previously described also apply to the bidirectionalwafer inserter. Reference is made to FIG. 30.

[0148] When inserting wafers connected via a tether, it is preferred touse the wafer inserter embodiment shown in FIG. 34 but the inserter maybe either fixed tip or detachable tip. (A cross-sectional view of thetrack used to deploy tethered wafer is provided in FIG. 57). The wafersare stacked in a cartridge in the wafer inserter. To position thewafers, the wafers are advanced along the top of the plunger and the endmost wafer is inserted at the bottom of the column. FIG. 39 shows thewafers 270 in the wafer inserter 272 being inserted into the surgicalsite. In order to remove the column 274, the bottom most wafer isremoved first. In FIG. 40, the entry port at the distal tip 276 of thewafer inserter 272 provides a fulcrum over which the tether slides. Thisensures that subsequent wafers are pulled down, then out of the waferinserter track without twisting relative to the track.

[0149] A number of options relating to both the wafer inserter and thewafers are available. FIGS. 4145 show wafers 280 having squared ends 282being inserted with a wafer inserter that lifts the leading wafer. Whenthe track 284 of the wafer inserter is placed in the prepared channel inthe surgical site, the wafer elevator 286 is in its down position, asseen in FIG. 41. A force (Fl) is applied to the wafers in the deliverychannel of the wafer inserter. FIG. 42 shows the first wafer 288advancing past the wafer elevator 286. The wafer elevator 286 flexes toallow the wafer 288 to pass into the lifting section of the waferinserter. The wafer 288 then proceeds to the distal stop 290 of thewafer inserter track 288, as seen in FIG. 43. The wafer elevator 286 isdrawn back slightly to clear the inserted wafer 288. As seen in FIG. 44,the elevator 286 is then advanced (F2) to engage the bottom surface 292of the newly inserted wafer 288. A force (F3) is applied to the waferinserter to advance another wafer 294 under the inserted wafer 288. Asthe wafer 294 is inserted it pushes the wafer elevator 286 to engage thewafer 288 or column of wafers previous inserted and elevates theproximal end 296 of the lower most wafer 288. The new wafer 294 is theninserted at the bottom of the column. FIG. 45 shows this processrepeated with consecutive wafers to create a column as may be desired.

[0150] As seen in FIG. 46, an alternate embodiment of the wafer inserterinvolves a wafer inserter 300 designed for inserting curved wafers 302.There may be surgical or structural advantages to inserting wafers thatare curved in a transverse plane. FIG. 46 also illustrates how a curvedwafer 302 may better fit the anatomy of the vertebral body.

[0151] Curved wafers may be inserted using either embodiment of thepreviously described wafer inserters (fixed tip or detachable tip) byincorporating a curved wafer track. The wafer and track are thenconfigured to have a constant radius. The instruments to prepare thevertebra for the inserter are similar to the ones described for thestraight inserter, but designed to function along a curve. The curve isset to approximately match the anterior curvature of the vertebral bodyand may be provided in a range of radii to accommodate patient sizevariation and variation in vertebral shape along the length of thespine. Alternatively, the curved wafer inserter can be configured todeploy wafers in opposing columns. The bidirectional deployment ofwafers may be independent, enabling the physician to increase eithercolumn as needed, or wafer deployment may be linked, in which case awafer would be inserted into each column simultaneously.

[0152] Distraction Device and Procedure Applied to Vertebral CompressionFractures

[0153] The ability to enter the vertebral body via an extrapedicularapproach dramatically increases the cross sectional size available forplacing a device into the vertebral body. Current extrapedicularsurgical techniques use a 6 mm ID cannula. According to the presentinvention, a rectangular cannula of approximately 4 mm to 12 mm in widthin a transverse plane and approximately 6 mm in height in a verticalplane can be placed into the lumbar and lower thoracic spine. Upperthoracic vertebrae, however, may be limited to a width of 3 mm to 8 mmin a transverse plane and a height of 3 mm to 6 mm in a vertical plane.

[0154]FIG. 47 illustrates an extrapedicular approach to a vertebral bodywherein an access channel 304 is placed through the posterolateral wallof the vertebral body. Other approaches may optionally be used forplacing the wafer inserter or inserters, although this may limit theaccess channel dimensions and corresponding implant size. FIG. 48illustrates a transpedicular approach to the vertebral body wherein anaccess cannula 306 is placed through the pedicle. In the extrapedicularapproach, cannulae may be placed bilaterally, through each pedicle.Similarly, two cannulae may be placed bilaterally using theextrapedicular approach, one on each side.

[0155] A preferred procedure for placing the wafers involves placing aguide wire into the vertebral body via an extrapedicular approach underfluoroscopy. An example guide wire 310 is illustrated in FIG. 49. Acannulated tamp is placed over the guide wire and advanced to thevertebral cortical wall. In one embodiment, as seen in FIG. 50, the tamp312 is cylindrical and is shown with a detachable handle 314. One methodof advancing the tamp into the vertebra involves tapping the tamp with ahammer or pushing/twisting the tamp by hand. Preferably, tampadvancement is monitored with a fluoroscope to place the distal tip ofthe tamp past the midline and spanning the midsection or anterior aspectof the vertebral body. Ideally, the tamp references or is indexed to theguide wire to minimize advancement of the tamp beyond the length of theguide wire. After advancing the tamp through the vertebral body to itsdesired position, the tamp is removed and the guide wire is left inplace.

[0156] An expandable access channel is advanced over the guide wire intothe vertebra through the opening created in the vertebral body. Again,the channel may reference the guide wire to prevent advancing thechannel beyond the length of the guide wire. Expanding the channelpermits adjustment of the channel to a size sufficient for receiving awafer inserter. FIG. 51 shows one embodiment of the expandable accesschannel 316 where two channels 318 and 320 are placed together withtheir open surfaces facing one another. FIG. 52 shows the two channels318 and 320 in a “closed” configuration, while FIG. 53 shows the twochannels 318 and 320 in an open configuration. The closed expandingchannel 316 is placed over the guide wire 310 and advanced into thevertebral body to the tip of the guide wire. The guide wire is removed.Position of the expanding channel and subsequent tapered and bluntexpanders should be monitored via fluoroscope. While an expandableaccess channel is specifically discussed and contemplated, it ispossible to use an access channel or series of channels which is notexpandable and which is at its fullest dimension before advancement intothe vertebra.

[0157] Once the expandable access channel is in place, the guide wiremay be removed. With the expandable access channel in place, a mandrelis placed inside the channel. The mandrel should be larger than thecollapsed channel in order to expand the channel as the mandrel isdriven distally. As seen in FIG. 54, the mandrel 322 may have a taperedend 324 for ease of deployment. Optionally, the mandrel may have a shapecorresponding with the shape of the access channel. Thus, when arectangular access channel is employed, a rectangular mandrel may beused. Advancing the mandrel through the length of the access channelexpands the open channels in a transverse plane creating a cavity in thevertebral body corresponding in shape to the shape of the expandedaccess channel. It is preferred that a second mandrel is provided with ablunt end in the event that the tapered end of the first mandrel doesnot fully expand the access channel. FIG. 55 depicts a blunt-end mandrel326. In either case, the mandrel should reference the access channel toprevent advancement of the mandrel beyond the length of the channel.Optionally, a series of sequentially larger mandrels may be used togradually enlarge the expanding channel. A hydraulic expansion device,or other suitable expansion device obvious to those skilled in the art,may alternately be used to enlarge the expanding channel.

[0158] In a first embodiment of the invention, the mandrel is removedfrom the expanded access channel and a wafer inserter is passed throughthe channel. The wafer inserter may be a track, preferably having a lipat its distal end for preventing the wafers from sliding too far intothe vertebra, and is inserted within the access channel. The distal endof the wafer inserter placed in the surgical site may be set by apositive stop at the proximal or distal end of the expandable accesschannel, or visually using fluoroscope. FIG. 3 illustrates a waferinserter track 64 in position in the vertebral body.

[0159] It is recommended to keep the access channel in position duringthe entire procedure. This will ensure minimal invasiveness of theprocedure. Removal of the access channel risks inability to locate thechannel already created.

[0160] The wafer inserter includes a plunger that slides within a trackfor advancing wafers down the track into the vertebral body. To positiona wafer in the vertebral body, a wafer is placed in the track and theplunger is advanced to full forward position to place the wafer at thedistal end of the track. To place a second wafer on the track, theplunger is retracted to the point where a second wafer drops from thecartridge of wafers to a position in front of the plunger. The plungeradvances the wafer to slide the second wafer underneath the first wafer.The force applied to the trailing edge of the second wafer causes thefirst wafer to be raised.

[0161] Various configurations of the wafer inserter and access channelare provided. As seen in FIG. 56, the wafer inserter track 330 passesthrough the expanded access channel 332. The track 330 is sized topermit only one wafer to pass there through. The plunger 334 is sized tofill the wafer inserter track's internal opening. Alternatively, theexpandable access channel 332 may be interchanged with a non-expandableor fixed dimension access channel.

[0162]FIG. 57, shows a wafer inserter and access channel configurationwherein the wafer inserter track 330 is sized for accommodating theplunger 334 with a wafer 336 resting on top of the plunger 334. Thewafers 336 are fed through the wafer track 330 on top of the plunger334. When the plunger 334 is retracted the length of one wafer, a waferdrops down in front of the plunger. When the plunger is advanced, thewafer is then inserted under the column of wafers. Simultaneously, awafer from the bottom of the column in the cartridge is advanced alongthe top of the plunger.

[0163]FIG. 37 shows a column 261 of wafers 263 being formed using adetachable tip wafer inserter 262, the tip 260 of which is detachablefrom the bulk of the wafer inserter 264. The process of inserting wafersis repeated with consecutive wafers until a column of sufficient heightis created to restore the vertebral body height per physiciandiscretion. During repetitions, vertebral body height and wafer positionshould be periodically checked via fluoroscope.

[0164] Alternately, a plurality of pre-stacked wafers may be inserted atonce as a stack. Multiple wafers may be inserted simultaneously to varythe thickness added to the column in a single step, each stack of wafersthus acting as a single wafer insertable unit. Multiple wafers added maybe of the same thickness or varying thicknesses. In this case, the waferinserter would provide an option to select one, two, three or morewafers to be inserted simultaneously. Once selected, the wafer inserterfeeds the stack of an appropriate number of wafers into the track andthe stack is advanced into the wafer column. The wafer inserter elevatesthe preceding wafer to facilitate insertion of multiple wafers. Waferstacks of any suitable size may be mixed to form a column in vivo.

[0165] If desired, the wafer inserter may be positioned intermediate totwo inserted wafers. That is, the wafer inserter may be positioned alongthe wafer column. Thus, a subsequently deployed wafer would be insertedintermediate to previously inserted wafers. In this embodiment, thewafer inserter may be configured for insertion of the wafer in avertical down direction, a vertical up direction, or any directionsuitable for forming a column with the previously inserted wafers.

[0166] In the example of vertebral compression fracture reduction, thecancellous bone below the wafer inserter may not provide adequatesupport for the wafer column when reducing the proximal end plate. Insuch situations, it may be advantageous to deploy wafers proximally atthe start while monitoring distal displacement of the wafer inserter. Ifthe wafer inserter displaces distally, then wafers may be inserteddistally to maintain the initial position of the wafer inserter.

[0167] Although the wafers may be straight or curved, straight waferswould likely provide the greatest surgical simplicity. Additionally,straight wafers more closely mimic current surgical techniques. However,a curved wafer requires a similar and only slightly modified techniqueof percutaneously placing a curved delivery instrument. The curved waferoffers an improved anatomic match between the wafer column and theanterior cortex of the vertebra, thereby increasing the surface area andavailable distraction force. Compression fractures typically involvecollapse of the superior end plate in a generally flat fashion rotatingabout a coronal axis at the superior aspect of the posterior vertebralwall.

[0168] A curved wafer inserter may enable placement of the wafer moreanterior in the vertebral body while increasing the implant surface areaand associated distraction force. In vertebral compression fractures,the superior end plate is often displaced distally at an oblique angleabout a coronal axis at the intersection of the superior end plate andthe posterior wall of the vertebral body. This results in compaction ofthe anterior cortical wall and the underlying cancellous bone. Placingcontoured wafers anteriorly to provide interior distraction that reducesthe superior end plate would be advantageous; the wafer column would bepositioned in a high weight bearing area of the vertebra.

[0169] When the fracture is reduced, or when the physician determinesthat an adequate number of wafers have been inserted, the wafer insertermay be removed with a removal plunger. The expanding access channel isleft in place. Alternatively, if the distal tip of the wafer inserter isdetachable, then upon removal of the wafer inserter, the tip is detachedand remains inserted in the vertebral body as part of the column. Again,the expanding access channel is left in place.

[0170] After an adequate column of wafers is inserted, bone filler maybe injected into the vertebra to encapsulate the wafers, provide weightbearing structure, and increase stability. The bone filler bonds thewafers to one another as well as to the filler mantle thatinterdigitates with the cancellous bone. The wafers may be solid inconstruction and thus require the filler to flow around the wafer columnand bond to the outer surfaces of the wafers. Wafer-to-wafer bonding isthen achieved through solvent activation of wafer interfaces viacapillary effect. Alternately, the wafers may include tunnels totransport bone filler through the wafer column and out to thesurrounding bone. Bone filler material would be injected into the wafercolumn and then flow through the column.

[0171] If bone filler is injected, an injection channel (340 of FIG.58), which may prefilled with bone filler, is advanced along the channelinto the vertebra. The bone filler should be allowed to thicken to thedesired consistency before injection into the vertebral space. Theinjection is preferably completed under fluoroscopic observation tomonitor bone filler flow. The total amount of filler injected is subjectto physician judgment. The physician may elect to use additionalinjection channel(s).

[0172] If the introduction of bone filler is desirable, the injectionchannel may be passed through the expandable access channel. Theinjection channel is advanced until it approximates the wafer column.The injection channel includes a channel through which the bone fillerflows, and a plunger to eject bone filler. FIG. 59 provides across-sectional view of the bone filler injection channel 340. The tipof the plunger 342 is of slightly larger cross-sectional area than theplunger 344. Thus, the plunger 344 is slightly smaller than the channel340 and is easily inserted there through. The tip 342 is large enough toensure complete coverage of the bone filler.

[0173] Once in position, the plunger on the bone filler delivery channelis advanced to inject the bone filling into and around the wafer columnand the surrounding cancellous bone. In the event that bone filler fromone delivery channel does not fill the vertebral body as per physician'sdiscretion, then additional delivery channels can be filled with bonefiller and bone filler delivered to the vertebral body in like fashion.Alternatively, any commercially available bone filler system may beused. Throughout the injection of bone filler, the vertebral bodyfilling should be monitored under fluoroscopic guidance in order toavoid extravasation.

[0174] Typically, the physician will have more control over cementdelivery and flow when the cement is delivered under low pressure.Delivering cement through larger cannula, either circular or rectangularin cross-section, will promote more uniform (laminar) flow at largerdelivery pressures. The current preference is to deliver cement througha cylindrical tube. The present invention enables use of a channel witha significantly larger cross-sectional area. For example, thecross-sectional area of a 6 mm ID tube is 28 mm². A rectangular tubewould enable up to a 6 mm vertical height and up to 12 mm in atransverse plane for a cross-sectional area of 82 mm². This provides amore than 150% increase in cross-sectional area.

[0175] The injection channel is left in place until the bone filler hasthickened sufficiently that it will not flow out of the injection holeupon removal of the injection channel. The injection channel and theaccess channel are removed. Alternatively, the wafer inserter may remainin place and the bone filler may be injected through that device or thebone filler may be injected through any commercially available bonefiller delivery system.

[0176]FIGS. 27 and 28 show two wafer column embodiments with cementinterdigitation and with cancellous bone around the wafer columns. Asseen in FIG. 28, the top and bottom wafers 198 and 200 respectively maybe configured larger than the intermediate wafers 202 of the wafercolumn 192. This facilitates full encapsulation of the wafers by thebone filler. Bone cement fills the space left around the wafer column192. Alternatively, as seen in FIG. 27, the wafers 194 of the wafercolumn 192 may be of constant size with bone cement filling the spacesurrounding the wafer column 192.

[0177] Another embodiment involves a wafer column built within apermeable membrane, the membrane having macro porosity. The membraneallows bone filler to flow through its wall into surrounding cancellousbone to provide better flow control, bone/filler interdigitation,stability, and structural support. Flow can thereby be controlled intosurrounding cancellous bone as well as on and into the wafer column.

[0178] The Distraction Device Applied to Tibial Plateau CompressionFractures

[0179] The current invention also provides an instrument that can placewafers in a vertical column to reduce tibial plateau compressionfractures through a minimally invasive approach. Thus, the implantsimultaneously reduces the fracture and stabilizes the fracture.

[0180] In treating isolated compression fractures of one or both tibialcondyles, a pathway to the underside of the depression is achieved byplacing a guide wire percutaneously to a position that traverses theunderside of the depression. The instrumentation for placing the implantis placed as described above in reference to vertebral compression. Thatis, a cylindrical tamp is advanced over the guide wire and then removedto allow an expandable channel to be placed and a wafer inserterpositioned therein. Alternatively, a fixed dimension access channel maybe used in place of the expandable channel.

[0181] Once in position, the wafer inserter places wafers in a verticalcolumn under the compression fracture. The wafers are inserted until thearticular surface is reduced (as confirmed by fluoroscopic orarthroscopic assessment). In treating an isolated tibial plateaucompression fracture, the wafers may be used alone, or with aninjectable bone filler material. The pathway through the tibial lateralwall may be filled with bone filler, or alternatively left to heal bynatural bone. In cases where both a compression fracture and a splittingfracture are present, the splitting fracture may be reduced andstabilized by minimally invasive placement of one or more bone screws.After stabilizing the splitting fracture, the compression fracture canbe reduced and stabilized as described for the isolated compressionfracture.

[0182] Alternatively, removable wafers may be inserted under thecompression fracture to reduce the fracture. Once reduced, the wafersare removed and the cavity created is filled with suitable bone fillermaterial, or with wafers fabricated from allograft bone or othersuitable bone substitute materials.

[0183] The Distraction Device Applied to Spinal Interbody Fusion

[0184] In performing spinal interbody fusion, the wafer inserter isplaced through the annular wall from a posterior approach, or aposterior-lateral approach. At least four procedures are contemplatedfor performing spinal interbody fusion with the wafer device. Theseinclude a posterior approach, a posterior lateral approach, an anteriorapproach, and an extrapedicular approach.

[0185] Surgical Procedure—Posterior Approach

[0186] The posterior approach, as shown in FIG. 60, involves two columnsof wafers each inserted lateral to a mid-sagittal plane. This ispreferably done using two wafer inserters 350 and 352 allowing gradualdistraction of the annulus in a parallel fashion. The wafer insertersmay be equipped with load sensors to provide a digital readout of theload being applied by each column of wafers. This enables improvedbalancing of the distraction forces on each side of the annulus.

[0187] Surgical exposure is made to the posterior of the spine to accessthe posterior aspect of the annulus. Preferably, two openings areprepared in the annulus, each lateral to the mid-sagittal plane. Theopenings may be a straight-line incision, or a “C” shaped incisionextending to the nucleus. The nucleus is then removed.

[0188] Bone spreaders/shavers are placed in the two openings and thevertebral bodies are distracted. The bone shaver or similar device isoperated to remove the central portion of the annulus. A generally flatsurface down to the bleeding bone of the superior and inferior endplatesis prepared. The end plates are decorticated down to bleeding bone.

[0189] The prepared surface supports the wafer columns. A wafer inserteris placed in each opening and used in the manner described above. It ispreferred to insert wafers in an alternating fashion between the twoinserters to uniformly distract the annulus.

[0190] Annular tension is monitored as an indication of stability. Whenadequate stability is achieved as per physician discretion, no furtherwafers are inserted and the wafer inserters are removed. After removal,the incisions may be closed using standard techniques.

[0191] Surgical Procedure—Posterior-Lateral Approach

[0192] In the case of a posterior-lateral approach, one wafer insertermay be used with a wafer sized to cover the prepared endplates ofopposing vertebral bodies.

[0193] A guide wire is percutaneously placed through theposterior-lateral surface of the annulus into the nucleus. An opening isprepared in the annulus by advancing a cylindrical cutter over the guidewire. An access channel is placed over the cutter and advanced to theannulus. Preferably, the access channel is then locked to the annulusand the guide wire and cutter are removed. The nucleus may then beextracted.

[0194] A bone spreader/shaver is placed through the access channel todistract the vertebral bodies. As in the posterior approach, the boneshaver or similar device is operated to remove the central portion ofthe annulus. A generally flat surface down to the bleeding bone of thesuperior and inferior endplates is prepared. The end plates aredecorticated down to bleeding bone.

[0195] The prepared surface supports the wafer column. A wafer inserteris placed through the access channel and used in the manner describedabove to insert wafers and distract the adjacent vertebral bodies.

[0196] Annular tension is monitored as an indication of stability. Whenadequate stability is achieved as per physician discretion, no furtherwafers are inserted and the wafer inserters are removed. After removal,the incisions may be closed using standard techniques.

[0197] Surgical Procedure—Extra-Pedicular Approach

[0198] A guide wire is percutaneously placed through theposterior-lateral wall of an adjacent vertebral body. The guide wireshould be angled in a fashion to enter the nucleus. A cylindrical tampis advanced to enlarge the opening. After the opening has been enlarged,an expanding access channel is placed over the tamp and advanced to thevertebral body. The access channel is locked to the vertebra and theguide wire and tamp are removed. The expanding access channel isenlarged to enable placement of a bone shaver and the wafer inserter.The nucleus may then be extracted.

[0199] As in the posterior-lateral approach, a bone spreader/shaver isplaced through the access channel to distract the vertebral bodies. Thebone shaver or similar device is operated to remove the disc's annulus.A generally flat surface down to the bleeding bone of the superior andinferior endplates is prepared. The end plates are decorticated down tobleeding bone.

[0200] The prepared surface supports the wafer column. A wafer inserteris placed through the access channel and used in the manner describedabove to insert wafers and distract the adjacent vertebral bodies. FIG.61 illustrates a wafer inserter 64 in position in a vertebral disc.

[0201] Annular tension is monitored as an indication of stability. Whenadequate stability is achieved as per physician discretion, no furtherwafers are inserted and the wafer inserters are removed. After removal,the incisions may be closed using standard techniques.

[0202] While a preferred embodiment of the present invention has beendescribed, it should be understood that various changes, adaptation andmodification may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

1. Method for distracting in a given direction two tissue surfaces,comprising consecutively inserting between the tissue surfaces aplurality of wafers to create a column of wafers, the column beingoriented between the tissue surfaces so as to expand in the givendirection as wafers are consecutively added to the column.
 2. The methodof claim 1 further including the step of creating a second column ofwafers oriented between the two tissue surfaces separate from the firstcolumn of wafers.
 3. The method of claim 1 further including the step ofconsecutively inserting between the tissue surfaces a plurality ofwafers to create another column of wafers, the column being orientedbetween the tissue surfaces so as to expand in a direction opposite thegiven direction as wafers are consecutively added to the column.
 4. Themethod of claim 1 including the step of inserting between the tissuesurfaces an elongated guide track along which the wafers travel duringinsertion.
 5. The method of claim 4 including the step of inserting eachwafer or stack of wafers subsequent to the first wafer or stack ofwafers between the next preceding wafer and a base.
 6. The method ofclaim 5 wherein the base is the guide track.
 7. The method of claim 5wherein the base is a wafer adjacent the next preceding wafer.
 8. Themethod of claim 5 wherein the wafers have leading and trailing beveledends, the method comprising the step of engaging the leading beveled endof one wafer with the trailing beveled end of the next preceding waferto enable the one wafer to be inserted between the guide track and thenext preceding wafer to thereby urge the preceding wafer away from theguide track in the given direction.
 9. The method of claim 5 includingthe step of urging the trailing edge of a first wafer away from thetrack to enable another wafer to be inserted between the base and thefirst wafer.
 10. The method of claim 8 or claim 9 including the step ofrestraining an inserted wafer from movement during insertion of a nextfollowing wafer along the track between the base and the inserted wafer.11. The method of claim 8 or claim 9 wherein the guide track includes anend portion upon which the wafers are stacked between the tissuesurfaces, the method comprising the step of uncoupling the end portionand removing the remainder of the guide track from between the tissuesurfaces while allowing the end portion to remain with the wafer column.12. The method of claim 6 including the step of lifting the first waferwith the guide track to allow the next preceding wafer to be insertedbetween the track and the first wafer.
 13. The method of claim 1including the step of providing a hardenable, fluent bone filler betweenthe tissue surfaces about and in contact with the wafer column.
 14. Themethod of claim 13 wherein one or more of the wafers havefiller-receiving orifices, the method including the step of providingthe fluent bone filler in the orifices.
 15. The method of claim 13wherein the wafers are so configured as to provide channels, grooves, orholes through and on the surface of each wafer when they are stacked,the method including the step of providing the fluent bone filler withinthe channels.
 16. The method of claim 15 wherein the wafer columnincludes orifices communicating the channels with each other, the methodcomprising the step of providing the fluent bone filler within thechannels and orifices.
 17. The method of claim 14 including the step ofproviding a membrane around the wafer column to control flow of thefluent bone filler into surrounding cancellous bone.
 18. The method ofclaim 14 including the step of providing a membrane around the wafercolumn to control flow of the fluent bone filler on and into the wafercolumn.
 19. The method of claim 4 wherein the elongated guide track iscurved generally in a plane normal to the given direction, the methodcomprising the step of consecutively inserting wafers curved so as tofollow the track to provide a curved wafer column.
 20. The method ofclaim 4 wherein the plurality of wafers are interconnected with aflexible tether.
 21. The method of claim 20 including the step ofremoving the wafer column by removing the last inserted wafer and usingthe connecting member to remove the earlier inserted wafers.
 22. Themethod of claim 20 wherein the tether is positioned along the wafers toprovide a continuous sliding surface to facilitate removal of the columnof wafers.
 23. The method of claim 20 wherein the wafers and theflexible tether are integrally formed.
 24. The method of claim 4 whereinthe tissue surfaces are part of a single bone, the method including thestep of forming an orifice within the bone and between the tissuesurfaces configured to enable insertion of the guide track.
 25. Themethod of claim 4 wherein the tissue surfaces are opposing surfaces oftwo bones, the method including the step of forming an orifice betweenthe opposing surfaces of the two bones configured to enable insertion ofthe guide track.
 26. The method of claim 4 including the step ofinserting between the tissue surfaces an elongated access channel withinwhich is received the guide track to afford access of the track betweenthe tissue surfaces.
 27. The method of claim 26 wherein the accesschannel has collapsed and expandable configurations, the methodincluding the steps of inserting the access channel in its collapsedconfiguration between the tissue surfaces and then expanding the accesschannel between the tissue surfaces laterally of its length and in adirection generally normal to the given direction to enable the accesschannel to receive the guide track.
 28. The method of claim 1 whereinadjacent wafers include a flexible tether extending between them, themethod including the step of withdrawing one wafer from between thetissue surfaces by withdrawing an adjacent wafer.
 29. The method ofclaim 1 including the step of applying a liquid to the wafers.
 30. Themethod of claim 29 wherein the liquid is a solvent carried in microspheres to enhance bonding wherein the micro spheres are ruptured duringinsertion of the wafer.
 31. The method of claim 1 including the step ofapplying a hardenable fluent designed for time-delayed activation. 32.The method of claim of claim 30 wherein the micro spheres furtherinclude an osteoinductive agent.
 33. The method of any one of claims1-32 wherein the wafers are curved in a plane generally normal to thegiven direction.
 34. The method of claim 1 wherein one or more wafersare of non-uniform thickness.
 35. The method of claim 34 wherein eachwafer has a length and a width and wherein one or more wafers increasesin thickness along the wafer length.
 36. The method of claim 34 whereineach wafer has a length and a width and wherein one or more wafersincreases in thickness along the wafer width.
 37. The method of any oneof claims 1-9 and 13-24, 26-36, wherein the tissue surfaces are superiorand inferior portions of a fractured vertebral body, the methodincluding the step of inserting consecutive wafers into the body of thevertebra between the superior and inferior portions to distract theportions generally in the direction of the vertebral axis until thenormal height of the vertebra is substantially attained.
 38. The methodof claim 1 further including the steps of consecutively insertingbetween the tissue surfaces a second plurality of wafers at a secondposition to create a second column of wafers, the column being orientedbetween the tissue surfaces so as to expand in the given direction aswafers are consecutively added to the column.
 39. Apparatus for thedistraction of tissue surfaces in a given direction, comprising aplurality of wafers stackable consecutively one upon another to form acolumn extending in the given direction, the wafers having top andbottom surfaces enabling them to move with respect to one another in asecond direction generally normal to the given direction as a wafercolumn is formed, and the wafers having opposed leading and trailingends so cooperatively beveled as to force the top surface of one waferto engage and ride beneath the bottom surface of another wafer when theleading edge of one wafer is urged in the second direction against thetrailing edge of another wafer.
 40. The apparatus of claim 39 whereinthe engaging wafer surfaces are provided with complementaryconfigurations restraining the wafers from slipping out of the column.41. The apparatus of claim 40 wherein the complementary configurationsare complementary ridges and grooves.
 42. The apparatus of claim 40wherein the complementary ridges and grooves have dovetail ridge andgroove configurations.
 43. The apparatus of claim 40 wherein thecomplementary configurations are configured to enable the wafers torotate in a plane normal to the given direction while remaining in thecolumn.
 44. The apparatus of claim 40 wherein the complementaryconfigurations comprise detent configurations so configured as torestrain any lateral movement between adjacent wafers in a column. 45.The apparatus of claim 40 wherein the complimentary configurationscomprise a cylindrical indent.
 46. The apparatus of claim 40 wherein thecomplimentary configurations comprise a spherical indent.
 47. Theapparatus of claim 40 wherein the wafers have top and bottom surfaces soconfigured as to permit limited rotation of one wafer with respect toanother wafer about an axis parallel to the second direction.
 48. Theapparatus of claim 40 wherein the wafers comprise a dovetail and acylindrical indent to constrain all degrees of freedom.
 49. Theapparatus of claim 39 wherein the wafers have cylindrical interfaces toprovide axial translation along the axis of the cylinder and rotationalmovement about the radius of the cylinder.
 50. The apparatus of claim 39wherein the wafers have spherical interfaces.
 51. The apparatus of claim39 further including a pin for locking the wafers in place.
 52. Theapparatus of claim 40 wherein the wafers have a top surface and a bottomsurface, the bottom surface having a leading edge, a trailing edge, andtwo lateral edges, the wafer further including a lip formed along thebottom surface for limiting axial travel of a subsequent wafer.
 53. Theapparatus of claim 52 wherein the lip extends along all edges of thebottom surface except for the trailing edge.
 54. The apparatus of claim52 wherein the lip extends along the leading edge of the bottom surface.55. The apparatus of claim 52 wherein the lip extends along the lateraledges of the bottom surface.
 56. The apparatus of claim 39 wherein thewafers are marked with a radio-opaque material for observation underfluoroscopy.
 57. The apparatus of claim 39 including a flexible tetherextending between consecutive wafers to facilitate withdrawal of wafersfrom between the tissue surfaces.
 58. The apparatus of claim 57 whereinthe wafers have an upper surface and a bottom surface and the tetherextends along the upper surface of the wafers.
 59. The apparatus ofclaim 57 in which the tether extends between the leading edge of onewafer and the trailing edge of the preceding wafer.
 60. The apparatus ofclaim 57 in which the tether extends between the trailing edge of onewafer and the trailing edge of the preceding wafer.
 61. The apparatus ofclaim 59 in which the tether is in the form of a web which, when thewafers are stacked, extends between adjacent wafers.
 62. The apparatusof any one of claims 39-61 wherein the wafers are curved in a planegenerally normal to the given direction.
 63. The apparatus of claim 39wherein one or more wafers are of non-uniform thickness.
 64. Theapparatus of claim 63 wherein each wafer has a length and a width andwherein one or more wafers increases in thickness along the wafer lengthsuch that the one or more wafers are configured as a wedge.
 65. Theapparatus of claim 63 wherein each wafer has a length and a width andwherein one or more wafers increases in thickness along the wafer widthsuch that the one or more wafers are configured as a wedge.
 66. Theapparatus of claim 39 where the wafers have a surface and furtherincluding a liquid on the surface of the wafers.
 67. The apparatus ofclaim 66 wherein the liquid is a solvent to enhance bonding.
 68. Theapparatus of claim 67 wherein the solvent is designed for time-delayedactivation.
 69. The apparatus of claim 39 wherein the wafers have asurface and further including a solvent carried in micro spheres on thesurface of the wafers to enhance bonding.
 70. The apparatus of claim 69wherein the micro spheres further include an osteoinductive agent. 71.The apparatus of claim 70 wherein the osteoinductive agents are designedfor time release.
 72. Apparatus for the distraction of tissue surfacesin a given direction, comprising a guide track having an end portioninsertable between the tissue surfaces, and a plurality of wafersconfigured to travel consecutively along the track to the end portion,the wafers and track being so configured as to form upon the end portiona stacked column extending in the given direction to distract the tissuesurfaces.
 73. The apparatus of claim 72 wherein the guide track isconfigured at its end portion to form a second stacked column of wafersextending in a direction opposite the given direction to distract thetissue surfaces.
 74. The apparatus of claim 72 wherein the wafers haveleading and trailing ends so configured as to enable each wafer afterthe first to slide between the guide track and the next preceding wafer.75. The apparatus of claim 72 wherein the wafers have leading andtrailing ends so configured as to enable each wafer after the first twowafers to slide between two previously inserted wafers.
 76. Theapparatus of claim 72 wherein the track is configured for positioningalong the wafer column and insertion of a wafer between two wafers inthe column.
 77. The apparatus of claim 72 wherein the wafers havebeveled leading and trailing ends such that each wafer after the firstto slides between the guide track and the next preceding wafer.
 78. Theapparatus of claim 72 including an elongated access channel within whichis received the guide track to afford access of the track between thetissue surfaces, and a plunger slidable along the track and configuredto engage the trailing end of a wafer and urge the leading end of thewafer distally.
 79. The apparatus of claim 78 wherein the access channelhas collapsed and expandable configurations.
 80. The apparatus of claim66 including a magazine containing the wafers and positioned to supplythe wafers to the track distally of the plunger.
 81. The apparatus ofclaim 66 wherein the wafers have top and bottom surfaces and are stackedin the magazine with a top surface of one wafer supporting the bottomsurface of an adjacent wafer.
 82. The apparatus of claim 80 wherein thewafers are aligned in the track with the leading edge of one waferadjacent the trailing edge of a preceding wafer.
 83. The apparatus ofclaim 72 wherein the track is configured to restrain each wafer fromfurther movement after the wafer is inserted and during insertion ofsubsequent wafers.
 84. The apparatus of claim 83 wherein the track has adistal edge and the wafers are restrained from further travel along thetrack by an upper lip of the track at its distal edge.
 85. The apparatusof claim 84 wherein the distal edge is movable for withdrawal of thetrack from the wafer column.
 86. The apparatus of claim 84 wherein thedistal edge is releasable for withdrawal of the track from the wafercolumn.
 87. The apparatus of claim 72 wherein the wafers are configuredto provide channels, grooves, or holes through and on the surface ofeach wafer for receiving fluent bone filler.
 88. The apparatus of claim72 further including a membrane around the wafer column to control flowof the fluent bone filler into surrounding cancellous bone.
 89. Theapparatus of claim 72 further including a force transducer for measuringthe force exerted by a wafer inserted into the column on the column. 90.The apparatus of claim 89 further including a display for displaying themeasured force.
 91. The apparatus of claim 89 further including anadjustable force guideline for column distraction force.
 92. Theapparatus of claim 72 further including a force transducer for measuringthe force exerted by the column on the tissue surfaces.
 93. Theapparatus of claim 92 further including a display for displaying themeasured force.
 94. The apparatus of claim 72 further including acounter for monitoring the number of wafers inserted into the column.95. The apparatus of claim 94 further including a display for displayingthe number of wafers.
 96. Kit for the distraction of tissue surfaces ina given direction, comprising: a plurality of insertable wafers; a guidefor forming a body access; a channel for expanding the body access; aninserter for inserting the wafers into the channel; a bone fillerinjection channel; and a sterile packaged tray containing the wafers,the guide, the channel, the inserter, and the bone filler injectionchannel.
 97. The kit of claim 96 further including bone filler.